Hm so for some reason this topic wasn’t here when I posted it earlier. Thoughts:

From what I understand (and I may be wrong: this isn’t my area), this invokes far more serious issues than you raise. The Bulletin of the Atomic Scientists wrote about the super-fuze upgrade (Mark 4A) in March, and argue that they are fundamentally tipping the balance in our supposedly MAD (Mutual Assured Destruction) world, creating the opportunity for a “successful” American first strike. They achieve this because the upgrade massively increases accuracy of detonation of these (relatively) small warheads, allowing them to target hardened targets (such as missile silos) with a much greater chance of success. This is only underlined by ever-improving American defensive weapons systems reducing enemies’ chances of doing the same. Add to this the Russian’s inferior early warning systems, and Russia seeing any attack both has less time to decide how to react, and must consider a much higher likelihood of an all-out strike: if they don’t retaliate within minutes, their ability to retaliate at all will be gone altogether.

This is a fairly terrifying asymmetry, and according to the article seems to have been achieved by the military without civilian oversight and without tickling international arms treaties.